Quarterly report pursuant to Section 13 or 15(d)

Service Revenue (Summary of PEO Pass-Through Costs Netted in Revenue) (Details)

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Service Revenue (Summary of PEO Pass-Through Costs Netted in Revenue) (Details) - USD ($)
$ in Millions
3 Months Ended 9 Months Ended
Feb. 29, 2024
Feb. 28, 2023
Feb. 29, 2024
Feb. 28, 2023
Revenue from Contract with Customer [Abstract]        
Payroll wages and payroll taxes $ 7,317.0 $ 6,944.1 $ 20,378.5 $ 19,615.2
State unemployment insurance (included in payroll wages and payroll taxes) 78.0 71.4 116.3 111.2
Guaranteed cost benefit plans $ 165.6 $ 157.8 $ 499.4 $ 494.8